1. Field of the Invention
The present invention relates to a direct injection type internal combustion engine with a low pressure fuel injector, in which a low pressure fuel, such as gasoline, light oil, benzene, ethyl and methyl alcohols, their mixed oil, or emulsion oils with water, air or other chemicals, is directly injected to a head wall or a top surface of the piston in the combustion chamber during the suction stroke, so that the present invention may ensure enough time for ebullition of the fuel, completely vaporize the fuel therefrom and then burn the vaporized fuel thereby to effect the combustion highly efficiently and to prevent the emission of unburned noxious gases such as hydrocarbon and the like.
2. Description of the Prior Art
Conventionally, an internal combustion engine of the type in which gasoline is directly injected into the combustion chamber and is ignited with an electric in what is called "Hesselman engine", has disadvantages since it injects the fuel during the compression stroke of the engine, it has to use a high pressure fuel injection device with an ignition device therefor so that the construction thereof is very complex and price thereof is very expensive. Also, gasoline droplets having a large particle diameter are supplied into the combustion chamber so that it has not been able to obtain the desired effects. Therefore, such a Hesselman engine has not been practically and widely used.
The most disadvantageous point of the prior art is the fact that sufficient ebullition time of the fuel cannot be ensured, because the fuel is injected into the combustion chamber at the end of the compression stroke of an engine.
In the case of a diesel engine, on the other hand, since it has a high compression ratio of 16 to 20, the pressure and temperature of air within the combustion chamber of the engine become high at the end of the compression stroke so that atomized light oil which is injected under high pressure conditions is ignited after a very short interval of the ignition delay of the engine.
However, in the case of a Hesselman engine it has a relatively low compression ratio of 8 to 12 so that the temperature of air within the combustion chamber at the end of the compression stroke is far lower than that in the case of the diesel engine. Therefore, in the Hesselman engine, it is difficult not only to ignite gasoline but also to completely vaporize all the gasoline. Moreover, as described above, since the fuel is injected at the end of the compression stroke, the injection timing of the gasoline is close to the top dead center and there is little time necessary for vaporization (or ebullition) of the fuel.
Accordingly, in the Hesselman engine, it is impossible to mix gasoline droplets in the gasoline vapor and to produce a reproducible and stable combustion condition.
The results of the ebullition rate estimated based on the conventional studies which have been conducted by the Invertor, are as shown in FIGS. 1 and 2, respectively.
FIG. 1 shows the time necessary for the gasoline droplets having a diameter of 100 microns to finish their ebullition during the suction stroke. While, FIG. 2 shows the time necessary for the gasoline droplets having a diameter of 100 microns to finish their ebullition during the compression stroke.
In FIG. 1, curve I is plotted for the case where the gasoline droplets are floating in hot gases under a pressure of 1 atm, whereas curve II is plotted for the case where the gasoline droplets in the hot gases under pressure 1 atm are brought into contact with the hot solid surface.
In FIG. 2, on the other hand, curve III is plotted in case the gasoline droplets are floating in hot gases under a pressure of 10 atms, whereas curve IV is plotted for the case where the gasoline droplets in the hot gases under pressure 10 atms are brought into contact with the hot solid surface.
In other words, the curves I and III illustrate the time necessary for the gasoline droplets having the diameter of 100 microns to be gasified while being floating in the hot gases.
Where the four-cycle engine is turned at 1500 r.p.m., its suction and compression strokes are completed for (60s/1500)/2.apprxeq.20 ms, respectively.
In the actual engine, on the contrary, since the average temperature and pressure of the mixture during the suction stroke are 70.degree. to 150.degree. C. and about 0.5 to 1 atm (ata), respectively, the time of 300.degree. to 160 ms is required for the complete ebullition. In the conventional internal combustion engine with a carburetor, as shown in FIGS. 3 and 4, little ebullition of the gasoline droplets takes place during the suction stroke and at the end thereof.
On the other hand, in a direct injection type internal combustion engine with a low pressure fuel injector according to the present invention which will be described later, as shown in FIGS. 5 and 6, the gasoline droplets are supplied to a head wall formed with a fin of a piston P' from an injection valve F for a short period in the form of atomization at the initial stage during the suction stroke, and is brought into contact with the head wall of the piston so that the gasoline droplets in the form of a jet begins to be instantly vaporized or boiled away (such a condition being called an ebullition, not an evaporation) thereby to be almost completely vaporized by the end of the suction stroke.
While, since the average temperature and pressure of the mixture during the compression stroke become about 325.degree. C. and about 10 atms (ata), respectively, the time of about 18 ms is required for the complete ebullition so that the ebullition can be almost finished during the compression stroke, assuming that the compression ratio is 8.5 and the average pressure and temperature within the combustion chamber are increased to 20 atms from 1 atm and to 560.degree. C. from 100.degree. C., respectively, during the compression stroke.
On the other hand, the times required for the ebullition for the case in which the gasoline droplets having the diameter of 100 microns come into contact with the hot solid surface are illustrated in the curve II for the suction stroke and in the curve IV for the compression stroke. Thus, the ebullition can be instantly finished if the temperature of the solid surface is raised close to the maximum ebullition rate as shown in the point a in FIG. 1. The point b appearing in FIG. 1 is the so-called "Leydenfrost" point. If the solid surface is maintained at the Leydenfrost point, the gasoline droplets do not form a liquid film on the solid surface, when they come into contact, but jump up in a round shape into the hot gases.
The experimental results thus far discussed are gathered for the gases under stationary conditions. In case the gases are flowing while becoming turbulent, the time necessary for the ebullition will be reduced to a few ten % of that in the stationary conditions.
Even in that case, however, it can be deduced that the time for ebullition is far shorter for the case of contacting with the solid surface than for the case of floating in the gases.
According to the experiments conducted by the Inventor, in the conventional direct injection type internal combustion engine in which the fuel is injected at the end of the compression stroke of the engine, the time required for ebullition of the fuel cannot be necessarily ensured because the fuel is injected during the compression stroke.
Accordingly, the Inventor has directed his attention to the above-mentioned points in order to solve these problems of the prior art and conducted various experiments according to his experiential philosophy that in a spark-ignition type internal combustion engine, the best performance of the engine can be obtained if all the liquid fuel is vaporized and burned. The present invention has been invented from these experiments for solving the aforementioned problems.